In RAN#66, a study item (RP-142307) was agreed with targets to study possible enhancements to RRM (Radio Resource Management) performance in high speed train environments. The justification is that there are railways such as Japan Tohoku Shinkansen (320 km/h), German ICE (330 km/h), AGV Italo (400 km/h), and Shanghai Maglev (430 km/h) in which vehicles travel at speeds greater than 300 km/h and where there is demand for using mobile services. The high speed scenario may further include mission critical (MC) operations involving high speed vehicles in the air. An example of an MC operation is Air Ground Air communications (also known as A2G communications) where high speed vehicles may include helicopters and planes containing wireless terminals. The A2G vehicles may be served by high speed radio nodes (also known as A2G base stations, A2G eNode Bs, etc.). Speeds of helicopters and planes may be in the order of 200-300 km/hr and 400-500 km/hr respectively.
In a corresponding motivation contribution (RP-141849), several scenarios of interest to operators are disclosed. In a number of these scenarios, a dedicated network is provided for railway coverage of the cellular system (either as a standalone network, or used in conjunction with a public network which is not specifically designed to provide high speed train coverage using carrier aggregation or dual connectivity).
LTE Mobility Scenarios
There are basically two kinds of mobility scenarios in LTE (Long Term Evolution) in a RRC (Radio Resource Control) state:                1) Idle state mobility, e.g., cell selection, cell reselection, etc.; and        2) Connected state mobility: handover, RRC connection re-establishment, RRC connection release with redirection, PCell or PCC (Policy and Charging Control) change in carrier aggregation (CA), etc.        
In both idle and connected states, the mobility decisions are typically based on at least one or more UE (also referred to as a wireless terminal, a mobile terminal, user equipment, a user equipment node, etc.) radio measurements, e.g., RSRP (Reference Signal Received Power), RSRQ (Reference Signal Received Quality), etc. In idle mode, the UE uses these measurements autonomously to reselect between cells, and in connected mode, the network controls mobility using measurement reports. The idle mode and connected state mobility in E-UTRAN (Evolved Universal Terrestrial Radio Access Network) could both be broadly classified into three main categories:                1) Intra-frequency mobility (in idle and connected states);        2) Inter-frequency mobility (in idle and connected states); and        3) Inter-RAT mobility towards, e.g., GSM, UTRAN, CDMA2000, WLAN, etc. (in idle and connected states).        
Radio Measurements
Several radio-related measurements may be used by the UE or the radio network node to establish and keep the connection and as well to ensure the quality of a radio link.
The measurements may be used in RRC idle state operations such as, cell selection, cell reselection (e.g., between E-UTRANs, between different RATs, and to non-3GPP RATs), and reduction/minimization of drive test (MDT). The measurements may also be used in RRC connected state operations, such as, for cell change (e.g., handover between E-UTRANs, handover between different RATs, and handover to non-3GPP RATs).
The UE may first have to detect a cell, and therefore, cell identification (e.g., acquisition of a physical cell identity or PCI) may also be a signal measurement. The UE may also have to acquire the cell global ID (CGI) of a node (or cell).
The RSRP and RSRQ may be used for at least RRM measurements such as for mobility, which include mobility in RRC connected state as well as in RRC idle state. The RSRP and RSRQ may also be used for other purposes, e.g., for enhanced cell ID positioning, minimization of drive test, etc.
In RRC connected state, the UE can perform intra-frequency measurements without measurement gaps. As a general rule, however, the UE may perform inter-frequency and inter-RAT measurements in measurement gaps unless it is capable of performing them without gaps. To enable inter-frequency and inter-RAT measurements for a UE requiring gaps, the network may have to configure measurement gaps. Two periodic measurement gap patterns (both with a measurement gap length of 6 ms) are defined for LTE:                1) Measurement gap pattern #0 with repetition period 40 ms; and        2) Measurement gap pattern #1 with repetition period 80 ms.The measurements performed by the UE are then reported to the network, which may use the measurements for various tasks.        
The radio network node (e.g., base station, also referred to as an eNB, eNodeB, an evolved NodeB, etc.) may also perform signal measurements. Examples of radio network node measurements in LTE include propagation delay between a UE and itself, UL (UpLink) SINR (signal-to-interference-plus-noise ratio), UL SNR (Signal-to-noise ratio), UL signal strength, Received Interference Power (RIP), etc. The eNB may also perform positioning measurements which are described in a later section below.
The UE may also perform measurements on the serving cell (also known as the primary cell) to monitor the serving cell performance. This is also referred to as radio link monitoring (RLM) or RLM related measurements in LTE. For RLM, the UE monitors the downlink link quality based on a cell-specific reference signal (CRS) in order to detect the downlink radio link quality of the serving or PCell.
In order to detect out of sync and in sync, the UE compares the estimated quality with the thresholds Qout and Qin respectively. The thresholds Qout and Qin are defined as the level at which the downlink radio link cannot be reliably received and respectively correspond to 10% and 2% block error rate of a hypothetical PDCCH (Physical Downlink Shared Channel) transmission.
Channel state indicator (CSI) related measurements (e.g., Channel Quality Indicator CQI, Pre-coding Matrix Indicator PMI, Rank Indicator RI, etc.) are performed by the UE on a serving cell or cells (e.g., PCell, PSCell, SCells, etc. in Carrier Aggregation CA) and reported to the network node. The network node uses these measurements for maintenance of the UE's serving cell performance, e.g., scheduling, link adaptation, rank adaptation, selection of precoder matrix, etc.
A wireless terminal may desirably modify operating parameters responsive to a speed of the wireless terminal. Existing methods of determining speeds of the wireless terminal, however, may introduce undesirable delay before modifying the operating parameters.